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b.
Hold meter about 15cm from the subject, point Lumigrid to each surface of the
subject and read the footcandle scale value.
c.
To determine the luminance range, it is sufficient to divide the highest meter
indication by the lowest. For example, if the highest value is 80 and the lowest 5, the
luminance range becomes 80/5 = 16/1 or 16 : 1.
3.
To obtain superior color photographs, determine upper and lower limits.
a.
Adequate color photographs can be obtained with typical color film if within the subject
luminance distribution, the maximum is less than 4 times the center point and minimum
more than 1 /4 times (i.e.: overall luminance range becomes less than 16 : 1).
b.
With a luminance center point of 20, if the measured maximum luminance is higher
than 80 (center point 20 x 4 = 80), color of that surface will become faded in the
photograph. Consequently, a slight reduction of incident light to this portion becomes
required.
c.
Conversely, a portion with a measured minimum luminance less than 5 (center point
20 / 4 = 5) requires increased illumination in order to obtain an acceptable color
photograph.
Luminance range measurement
28
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